Use of garden organic compost in a long-term vegetable field trial: biological soil health

Alternative management practices need to be developed to improve the sustainability of intensive vegetable production in peri-urban areas. A field trial was established in 2005 at Camden, near Sydney, Australia to evaluate the effect of garden organic compost on vegetable production and soil quality relative to conventional practice and under low and high soil P status. The trial comprised seven treatments; compost (garden organic), conventional practice (fertiliser and poultry manure) and a mixture of compost and inorganic fertiliser, all replicated at high and low soil P, plus a nil control. Compost was applied once at the beginning of the trial and again before the 6 th crop (125 dry t/ha/application). Results are reported for 7 consecutive vegetable crops: broccoli, eggplant, cabbage, capsicum, leek, capsicum and broccoli. Production and crop quality parameters were recorded. Soil samples were collected and chemical, physical and biological properties analysed at the time of planting all crops and prior to harvest for crops 4 to 6. Soil biological indicators measured include basal respiration, microbial biomass carbon, hydrolysis of fluorescein diacetate (FDA) and fungal DNA. Compost application significantly increased soil respiration in the first crop but the benefit was diminished in subsequent crops. The response was more pronounced in the crop soils following the second compost application with respiration, biomass and FDA higher in the compost treatments. Preliminary DNA analysis of soil samples collected in the second capsicum crop found a greater diversity of fungal organisms in the low P compost treatment. Future work will look at expanding the assessment of soil biological indicators and the potential for pathogen suppression.